U.S. patent number 10,025,293 [Application Number 15/303,860] was granted by the patent office on 2018-07-17 for object production.
This patent grant is currently assigned to BAE Systems plc. The grantee listed for this patent is BAE Systems plc. Invention is credited to John Bickerstaff, David Mark Wilson.
United States Patent |
10,025,293 |
Bickerstaff , et
al. |
July 17, 2018 |
Object production
Abstract
Disclosed is a method of producing an object, the method
comprising: providing a workpiece comprising a plurality of
attachment features for attaching the workpiece to a machining
fixture; determining a datum, the datum being dependent upon the
relative positions of the attachment features; measuring the
surface of the workpiece with respect to the datum; providing the
machining fixture; attaching, using the attachment features, the
workpiece to the machining fixture; providing a digital model
specifying the object including the attachment features; and,
thereafter, using the measurements of the workpiece surface and the
digital model, controlling machining apparatus with respect to the
datum to machine the workpiece so as to produce the object as
specified by the digital model.
Inventors: |
Bickerstaff; John (Lancashire,
GB), Wilson; David Mark (Lancashire, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
BAE Systems plc |
London |
N/A |
GB |
|
|
Assignee: |
BAE Systems plc (London,
GB)
|
Family
ID: |
52946631 |
Appl.
No.: |
15/303,860 |
Filed: |
April 10, 2015 |
PCT
Filed: |
April 10, 2015 |
PCT No.: |
PCT/GB2015/051090 |
371(c)(1),(2),(4) Date: |
October 13, 2016 |
PCT
Pub. No.: |
WO2015/162400 |
PCT
Pub. Date: |
October 29, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170036780 A1 |
Feb 9, 2017 |
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Foreign Application Priority Data
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|
|
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Apr 24, 2014 [EP] |
|
|
14275090 |
Apr 24, 2014 [GB] |
|
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1407184.9 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64F
5/10 (20170101); G05B 19/4097 (20130101); G05B
19/4099 (20130101); G05B 2219/35134 (20130101) |
Current International
Class: |
B64F
5/00 (20170101); G05B 19/4099 (20060101); B64F
5/10 (20170101); G05B 19/4097 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
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19900950 |
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May 2000 |
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1139189 |
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Oct 2001 |
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EP |
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1230124 |
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Dec 2005 |
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EP |
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1952972 |
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Jun 2008 |
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EP |
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2772427 |
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Mar 2014 |
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EP |
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2703919 |
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May 2014 |
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EP |
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2788743 |
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Jul 2000 |
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FR |
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2350809 |
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Dec 2000 |
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GB |
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2441226 |
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Feb 2008 |
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GB |
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199850180 |
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Nov 1998 |
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WO |
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0136270 |
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May 2001 |
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WO |
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20010036270 |
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May 2001 |
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WO |
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2014046783 |
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Mar 2014 |
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WO |
|
Other References
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|
Primary Examiner: Pan; Yuhui R
Attorney, Agent or Firm: Maine Cernota & Rardin
Claims
What is claimed is:
1. A method for producing a system, the method comprising:
providing a workpiece comprising a plurality of attachment features
for attaching the workpiece to a machining fixture, said machining
fixture comprising a plurality of fixture receiving elements for
receiving the attachment features of the workpiece, the relative
positions of the fixture receiving elements being dependent upon
the relative positions of the attachment features; determining a
datum, the datum being dependent upon relative positions of the
attachment features, said determining the datum including measuring
the relative positions of the fixture receiving elements on the
machining fixture and using the measurements of the relative
positions of the fixture receiving elements, calculating the datum;
measuring a surface of the workpiece with respect to the datum;
providing the machining fixture; attaching, using the attachment
features, the workpiece to the machining fixture; providing a
digital model specifying a component of the system, the digital
model including the attachment features; using the measurements of
the workpiece surface and the digital model, controlling the
machining apparatus with respect to the datum to machine the
workpiece attached to the machining fixture so as to produce the
component as specified by the digital model; removing the component
from the machining fixture; providing an assembly tool; attaching,
using the attachment features, the component to the assembly tool;
and performing an assembly operation on the component, thereby
producing the system.
2. The method according to claim 1, wherein the system is at least
part of an airframe of an aircraft.
3. The method according to claim 2, wherein the system is at least
part of an airframe aft fuselage.
4. The method according to claim 1, wherein the component is an
airframe component selected from the group of airframe components
consisting of a frame and a longeron.
5. The method according to claim 1, wherein: the system is
configured for attachment to a further system; and the step of
providing the assembly tool comprises: determining a position and
orientation relative to the further system that the component would
have if the system was attached to the further system; using the
determined position and orientation of the component relative to
the further system, determining one or more positions and
orientations relative to the further system at which the component
is to be supported; providing a jig frame; attaching, to the jig
frame, a reference structure; providing a plurality of pickup
devices each having a pickup receiving element for receiving a
component of the system; and securing each pickup device to the jig
frame such that each pickup receiving element is at a predetermined
position and orientation relative to the reference structure that
will position the component at the determined position and
orientation relative to the further system at which the component
is to be supported.
6. The method according to claim 1, wherein the step of determining
the datum comprises: measuring the relative positions of the
attachment features on the workpiece; and using the measurements of
the relative positions of the attachment features, calculating the
datum.
7. The method according to claim 1, wherein the step of providing
the machining fixture comprises: providing an initial machining
fixture; providing a further digital model specifying the machining
fixture; and using the further digital model and the datum,
controlling machining apparatus with respect to the datum to
machine the initial machining fixture so as to produce the
machining fixture as specified by the further digital model.
8. The method according to claim 1, wherein the machining fixture
comprises one or more reference surfaces, each reference surface
being associated with a component feature; and machining the
workpiece comprises, for each reference surface: locating at least
part of the machining apparatus against that reference surface; and
controlling the machining apparatus to move away from that
reference surface with respect to the datum to machine the
workpiece so as to form the component feature associated with that
reference surface.
9. The method according to claim 8, wherein the step of providing
the machining fixture comprises: providing an initial machining
fixture; providing a further digital model specifying the machining
fixture; and using the further digital model and the datum,
controlling machining apparatus with respect to the datum to
machine the initial machining fixture so as to produce the
machining fixture as specified by the further digital model; and
the step of providing the further digital model comprises: using
the digital model of the component, identifying one or more
component features; for each identified component feature,
determining a position and orientation of a reference surface
thereof relative to the datum; and using the determined a positions
and orientations of the one or more reference surfaces, determining
the further digital model.
10. An apparatus for producing a system that incorporates a
component formed from a workpiece comprising a plurality of
attachment features, the apparatus comprising: a machining fixture
configured to receive the workpiece at the attachment features,
said machining fixture comprising a plurality of fixture receiving
elements for receiving the attachment features of the workpiece,
the relative positions of the fixture receiving elements being
dependent upon the relative positions of the attachment features;
one or more processors configured to determine a datum, the datum
being dependent upon relative positions of the attachment features,
said determining of the datum including measuring the relative
positions of the fixture receiving elements on the machining
fixture and using the measurements of the relative positions of the
fixture receiving elements, calculating the datum; measurement
apparatus suitable for measuring a surface of the workpiece with
respect to the datum; machining apparatus being configured to,
using the measurements of the workpiece surface and a digital model
specifying the component of the system including the attachment
features, be controlled so as to machine the workpiece attached to
the machining fixture so as to produce the component as specified
by the digital model; an assembly tool configured to receive the
component at the attachment features; and an assembly apparatus
suitable for performing an assembly operation on the component on
the assembly tool, thereby producing the system.
11. The apparatus according to claim 10, wherein the system is at
least part of an airframe of an aircraft.
12. The apparatus according to claim 11, wherein the system is at
least part of an airframe aft fuselage.
13. A system produced using the method according to claim 1.
14. The system according to claim 13, wherein the system is at
least part of an airframe aft fuselage.
Description
RELATED APPLICATIONS
This application is a national phase application filed under 35 USC
.sctn. 371 of PCT Application No. PCT/GB2015/051090 with an
International filing date of Apr. 10, 2015 which claims priority of
GB Patent Application 1407184.9 filed Apr. 24, 2014 and EP Patent
Application 14275090.0 filed Apr. 24, 2014. Each of these
applications is herein incorporated by reference in its entirety
for all purposes.
FIELD OF THE INVENTION
The present invention relates to methods of producing objects.
BACKGROUND
Aircraft airframes typically comprise a plurality of frames (or
formers) and longerons (or stringers/stiffeners). The frames are
typically laterally spaced from one another and arranged
perpendicular to the longitudinal axis of the aircraft. The primary
purpose of formers is to establish the shape of the fuselage and
reduce the column length of the longerons. The longerons are
typically elongate members which are attached to the frames and are
arranged parallel to the longitudinal axis of the aircraft. The
longerons support the aircraft skin and, in use, transfer
aerodynamic loads acting on the skin onto the frames.
It is desirable that aircraft airframes are produced to be within
very tight tolerance bounds.
Production of an aircraft airframe typically comprises producing
two or more separate airframe sections (for example, a fore
fuselage section, an aft fuselage section, and a tail section), and
subsequently attaching those sections together.
It tends to be very difficult to produce separate airframe sections
with a sufficient level of precision to allow for easy assembly of
the airframe. Lengthy and expensive shimming processes may be
required to fill gaps between the airframe sections when those
sections are attached together.
Production of a section of an aircraft airframe typically involves
the use of airframe assembly tools designed to support airframe
components while they are being worked on and to locate different
components together in the correct relative positions during
airframe assembly. Traditionally, each different assembly process
has required at least one dedicated assembly tool, which is
produced specifically for a given set of components and which is
designed to support the components in a particular manner so that
assembly operations can be carried out without interference from
the tool. Such assembly tools are manufactured to exacting
standards.
A conventional assembly tool comprises a rigid metal jig whose
framework is constructed from welded box section steel. A plurality
of pick-up devices is mounted on the framework for carrying the
aircraft components during the assembly process, and these too are
conventionally produced from welded steel parts.
EP 1 230 124 discloses such an assembly tool.
SUMMARY OF THE INVENTION
In a first aspect, the present invention provides a method of
producing an object, the method comprising: providing a workpiece
comprising a plurality of attachment features for attaching the
workpiece to a machining fixture; determining a datum, the datum
being dependent upon the relative positions of the attachment
features; measuring the surface of the workpiece with respect to
the datum; providing a machining fixture; attaching, using the
attachment features, the workpiece to the machining fixture;
providing a digital model specifying the object including the
attachment features; and thereafter, using the measurements of the
workpiece surface and the digital model, controlling machining
apparatus with respect to the datum to machine the workpiece so as
to produce the object as specified by the digital model.
The machining of the workpiece is performed with respect to the
datum. Thus, object features (e.g. the surface) of the object are
produced with respect to the attachment features of the object. The
attachment features of the object tend to be those points on the
workpiece that are most securely held by the machining fixture.
Thus all object features are machined with respect to a secure
datum and hence tend to be produced with high accuracy with respect
to one another.
The object may be a component part of a system and the plurality of
attachment features are further configured to attach the object to
an assembly tool during a process of assembling the system.
The object may be a component of an airframe selected from the
group of airframe components consisting of a frame and a
longeron.
The step of determining the datum may comprise measuring the
relative positions of the attachment features on the workpiece,
and, using the measurements of the relative positions of the
attachment features, calculating the datum.
The machining fixture may comprise a plurality of receiving
elements for receiving the attachment features of the workpiece,
the relative positions of the receiving elements being dependent
upon the relative positions of the attachment features. The step of
determining the datum may comprise measuring the relative positions
of the receiving elements on the machining fixture, and, using the
measurements of the relative positions of the receiving elements,
calculating the datum.
The step of providing the machining fixture may comprise: providing
an initial machining fixture; providing a further digital model
specifying the machining fixture; and, using the further digital
model and the datum, controlling machining apparatus with respect
to the datum to machine the initial machining fixture so as to
produce the machining fixture as specified by the further digital
model.
The machining fixture may comprise one or more reference surfaces,
each reference surface being associated with an object feature.
Machining the workpiece may comprise, for each reference surface,
locating at least part of the machining apparatus against that
reference surface and controlling the machining apparatus to move
away from that reference surface with respect to the datum to
machine the workpiece so as to form the object feature associated
with that reference surface.
The step of providing the further digital model may comprise: using
the digital model of the object, identifying one or more object
features; for each identified feature, determining a position and
orientation of a reference surface relative to the datum; and,
using the determined a positions and orientations of the one or
more reference surfaces, determining the further digital model.
In a further aspect, the present invention provides an assembly
process for producing a system, the assembly process comprising:
producing an object according to the preceding aspect; providing an
assembly tool; attaching, using the attachment features of the
object, the object to the assembly tool; and performing an assembly
operation on the at least one objects, thereby producing the
system.
The system may be at least part of an airframe of an aircraft and
the object is a component part of the at least part of an
airframe.
The system may be for attachment to a further system. The step of
providing the assembly tool may comprise: determining, when the
system is attached to a further system, a position and orientation
of the object relative to the further system; using the determined
position and orientation of the object relative to the further
system, determining one or more positions and orientations relative
to the further system at which the object is to be supported;
providing a jig frame; attaching, to the jig frame, a reference
structure; providing one or more plurality of pickup devices, each
having a receiving element for receiving a component of the system;
and securing each pickup device to the jig frame such that a
position and orientation relative to the reference structure of
each receiving element is the same as a respective determined
position and orientation relative to the further system at which
the object is to be supported.
In a further aspect, the present invention provides apparatus for
producing an object, the apparatus comprising: means for providing
a workpiece, the workpiece comprising a plurality of attachment
features for attaching the workpiece to a machining fixture; one or
more processors configured to determine a datum, the datum being
dependent upon the relative positions of the attachment features;
measurement apparatus for measuring the surface of the workpiece
with respect to the datum; a machining fixture configured to
receive the workpiece; and machining apparatus configured to, using
the measurements of the workpiece surface and a digital model the
object including the attachment features, be controlled with
respect to the datum so as to machine the workpiece so as to
produce the object as specified by the digital model.
In a further aspect, the present invention provides an object
produced using a method according to any of the preceding
aspects.
In a further aspect, a system produced using a method according to
any of the preceding aspects. The system may be an aircraft.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration (not to scale) of an example
aircraft;
FIG. 2 is a schematic illustration (not to scale) of a portion of
an airframe of an aft fuselage of the aircraft;
FIG. 3 is a schematic illustration (not to scale) showing a side
view of a first frame;
FIG. 4 is a process flow chart showing certain steps of a process
of producing the first frame;
FIG. 5 is a schematic illustration (not to scale) of a perspective
view of a frame machining fixture;
FIG. 6 is a schematic illustration (not to scale) showing a
top-down view of a workpiece coupled to the frame machining
fixture;
FIG. 7 is a process flow chart showing certain steps of an
embodiment of a process of producing the airframe;
FIG. 8 is a schematic illustration (not to scale) showing a
perspective view of an embodiment of an assembly jig;
FIG. 9 is a schematic illustration (not to scale) showing packer
material applied to an outer surface of the components of the
airframe;
FIG. 10 is a schematic illustration (not to scale) showing an
example way in which the packer material may be applied to a
surface of an airframe component;
FIG. 11 is a schematic illustration (not to scale) showing a
further example way in which the packer material may be applied to
a surface of an airframe component; and
FIG. 12 is a process flow chart showing certain steps of an
embodiment of a process of producing the jig.
DETAILED DESCRIPTION
It will be appreciated that relative terms such as horizontal and
vertical, top and bottom, above and below, front and back, upper
and lower, and so on, are used herein merely for ease of reference
to the Figures, and these terms are not limiting as such, and any
two differing directions or positions and so on may be implemented
rather than truly horizontal and vertical, top and bottom, and so
on.
FIG. 1 is a schematic illustration (not to scale) of an example
aircraft 2 comprising an aft fuselage 4, and an aircraft fore
section 5. The aircraft fore section 5 includes a central fuselage
to which the aft fuselage 4 is attached.
The aft fuselage 4 comprises an airframe and an aircraft skin
fastened to the airframe. In this embodiment, the aft fuselage 4
comprises a port boom and a starboard boom that are mechanically
attached together along a centreline. Each boom of the aft fuselage
4 comprises a plurality of structural components (for example,
frames, keels, longerons, and skins) that are mechanically attached
together.
FIG. 2 is a schematic illustration (not to scale) of a portion of
the airframe 6 of the aft fuselage 4.
In this embodiment, the airframe 6 comprises three laterally
spaced-apart frames or "formers", namely a first frame 8, a second
frame 10, and a third frame 12; three longerons, namely a first
longeron 14, a second longeron 16, and a third longeron 18; and a
beam 20. For reasons of clarity, the longerons 14, 16, 18 and the
beam 20 are shown as hashed in FIG. 2.
In this embodiment, the frames 8, 10, 12 are made of aluminium or
titanium. The frames 8, 10, 12 define the shape of the aircraft
fuselage and, in use, provide stability to the aircraft 2 by
preventing or opposing deflection of the longerons 14, 16, 18. When
the aircraft 2 is fully assembled, the frames 8, 10, 12 are
arranged substantially perpendicularly to the longitudinal axis of
the aircraft 2
In this embodiment, the longerons 14, 16, 18 are made of aluminium
or titanium. The longerons 14, 16, 18 are elongate members to which
the skin of the aircraft is fastened. When the aircraft 2 is fully
assembled, the longerons 14, 16, 18 run substantially parallel to
the longitudinal axis of the aircraft 2. In this embodiment, the
longerons 14, 16, 18 are fastened to the frames 8, 10, 12 by a
plurality of bolts. In this embodiment, the first longeron 14 has a
first end 14a attached to the first frame 8 and a second free end
14b proximate to the third frame 12. Similarly, the second longeron
16 has a first end 16a attached to the first frame 8 and a second
free end 16b proximate to the third frame 12. Similarly, the third
longeron 18 has a first end 18a attached to the first frame 8 and a
second free end 18b proximate to the third frame 12.
In this embodiment, during assembly of the aircraft 2, the second
free ends 14b, 16b, 18b of the longerons 14, 16, 18 are attached to
the fore fuselage 5 of the aircraft 2. In particular, the second
free ends 14b, 16b, 18b of the longerons 14, 16, 18 are attached to
a frame of the fore fuselage 5. This frame of the fore fuselage 5
to which the second free ends 14b, 16b, 18b of the longerons 14,
16, 18 are to be attached is hereinafter referred to as the "fore
fuselage frame".
In this embodiment, the beam 20 is made of aluminium or titanium.
The beam 20 is an elongate member. The beam 20 is attached at its
first end (i.e. a proximal end) to the first frame 8 by a plurality
of bolts, and extends away from the frames 8, 10, 12 to its second
end (i.e. a distal free end) opposite to its first end. When the
aircraft 2 is fully assembled, the beam 20 runs substantially
parallel to the longitudinal axis of the aircraft 2.
In this embodiment, in addition to being attached together by the
longerons 14, 16, 18, the frames 8, 10, 12 are attached together by
further structural elements often called "keels" which are located
between adjacent frames 8, 10, 12. For ease of illustration and
clarity, these keels are not shown in FIG. 2.
In this embodiment, to produce the aft fuselage 4, a composite
aircraft skin is fastened to the airframe 6. The outer shape of the
assembled aft fuselage 4 (i.e. the outer shape of the aft fuselage
4 produced by fastening the composite skin to the airframe 6) is
hereinafter referred to as the Outer Mould Line (OML) of the aft
fuselage 4. In this embodiment, the OML of the aft fuselage 4 is to
be within a pre-specified tolerance. The OML of the aft fuselage 4
having the required tolerance is facilitated by the Inner Mould
Line (IML) of the aft fuselage 4 being within a pre-specified
tolerance. The IML of the aft fuselage 4 is the surface at which
the airframe 6 and the aircraft skin abut, i.e. an outer surface of
the airframe 6 and inner surface of the aircraft skin.
An embodiment of a process of producing the airframe 6 is described
in more detail later below with reference to FIG. 7.
FIG. 3 is a schematic illustration (not to scale) showing a side
view of the first frame 8.
The first frame 8 comprises a plurality of longeron landings 30a-c
to which, during assembly of the airframe 4, the longerons 14, 16,
18 are fastened. In particular, the first frame 8 comprises a first
longeron landing 30a shaped to receive a portion of the first
longeron 14, a second longeron landing 30b shaped to receive a
portion of the second longeron 16, and a third longeron landing 30c
shaped to receive a portion of the third longeron 18. The longeron
landings 30a-c are attachment features to which other components,
in particular the longerons 14-18, attach.
The first frame 8 further comprises a plurality of fixture
attachment features 32. In this embodiment, there are four fixture
attachment features 32. As described in more detail later below,
the fixture attachment features 32 are for attaching the first
frame 8 to a fixture such as a machining fixture and/or an assembly
fixture. In this embodiment, the fixture attachment features 32 are
holes through the structure of the first frame 8 through which
locator pins or other elongate members may be positioned.
In this embodiment, similarly to the first frame 8, the second
frame 10 also comprises three longeron landings, each longeron
landing being configured to receive a portion of a respective
longeron 14, 16, 18. Also, the second frame 10 comprises a
plurality of fixture attachment features.
In this embodiment, similarly to the first and second frames 8, 10,
the third frame 12 also comprises three longeron landings, each
longeron landing being configured to receive a portion of a
respective longeron 14, 16, 18. Also, the third frame 12 comprises
a plurality of fixture attachment features.
FIG. 4 is a process flow chart showing certain steps of a process
of producing the first frame 8. A similar process, mutatis
mutandis, may be used to produce the second and third frames 10,
12. A similar process, mutatis mutandis, may be used to produce the
beam 20. A similar process, mutatis mutandis, may be used to
produce the longerons 14, 16, 18.
At step s2, a human designer generates or creates a digital model,
hereinafter referred to as the "first digital model". The first
digital model is of the first frame 8. This may be performed using
a computer and an appropriate software package, for example, the
Catia (Trademark) V4 software package. The first digital model may
defined using a digital model of the airframe 6 or aft fuselage
4.
At step s4, the human designer generates or creates a further
digital model, hereinafter referred to as the "second digital
model". The second digital model is of a frame machining fixture.
The frame machining fixture is a fixture system that is to be used
to secure a workpiece in place whilst that workpiece is machined to
form the first frame 8. The frame machining fixture will be
described in more detail later below with reference to FIG. 5.
At step s6, a forging system produces a first forging. The first
forging is an aluminium blank from which the first frame 8 is to be
produced. A digital model of the first forging may be used to
produce the first forging. This digital model may be defined using
a digital model of the airframe 6 or aft fuselage 4.
At step s8, using the first digital model, a 5-axis computer
numerical control (CNC) milling machine machines the first forging
to produce a workpiece from which the first frame 8 is to be
produced.
In this embodiment, the workpiece is essentially the same shape as
the first frame 8 except that the workpiece comprises additional
material where the longeron landings 30a-c are to be located. The
workpiece comprises the fixture attachment features 32. The
workpiece will be described in more detail later below with
reference to FIG. 5.
At step s10, the forging system produces a second forging. The
second forging is a steel blank from which the frame machining
fixture is to be produced. In other embodiments, the blank from
which the frame machining fixture is to be produced is a structure
created by bolting or welding a plurality of substructures
together. A digital model of the second forging may be used to
produce the second forging. This digital model may be defined using
a digital model of the airframe 6 or aft fuselage 4.
At step s12, using the second digital model, the 5-axis CNC milling
machine machines the second forging so as to produce the frame
machining fixture. In other embodiments, the frame machining
fixture is created by bolting or welding a plurality of
substructures together. The first digital model may also be used in
the production of the frame machining fixture.
FIG. 5 is a schematic illustration (not to scale) of a perspective
view of the frame machining fixture 40.
In this embodiment, the frame machining fixture 40 comprises a
substantially rigid base portion 41, a plurality of locator pins
42, and a plurality of precision ground blocks 44a-c.
In this embodiment, there are four locator pins 42. The locator
pins 42 are located on an upper surface of the base portion 41 and
extend away from the upper surface of the base portion 41 in a
direction that is substantially perpendicular to that surface. In
this embodiment, each of the locator pins 42 is configured to
couple to a respective fixture attachment feature 32 of the
workpiece. The relative positions of the locator pins 42 correspond
to those of the fixture attachment features 32 such that the
workpiece may be placed onto the upper surface of the base portion
41 in such a way that each locator pin 42 couples to a respective
fixture attachment feature 32, thereby securing the workpiece
against the frame machining fixture 40. The workpiece and the frame
machining fixture 40 are complementary. The locator pins 42 are
configured to securely hold the workpiece to prevent or oppose
movement or deflection of the workpiece while the workpiece is
being machined.
In this embodiment, the first and second digital models are created
concurrently. This tends to facilitate in the production of the
complementary workpiece and the frame machining fixture 40.
In this embodiment, there are three blocks 44a-c, namely a first
block 44a, a second block 44b, and a third block 44c. The blocks
44a-c are located on an upper surface of the base portion 41 and
extend away from the upper surface of the base portion 41 in a
direction that is substantially perpendicular to the upper surface
of the base portion 41. In this embodiment, the locations of the
blocks 44a-c are such that, when the workpiece is coupled to the
frame machining fixture 40 by locating the locator pins 42 in the
fixture attachment features 32, each block 44a-c is proximate to a
respective surface of the workpiece that is to be machined so as to
form a longeron landing 30a-c. Furthermore, each block 44a-c
includes a surface that is substantially parallel with a respective
surface of the workpiece that is to be machined so as to form a
longeron landing 30a-c. In particular, the first block 44a is
proximate to and substantially parallel with the surface of the
workpiece that is to be machined so as to form the first longeron
landing 30a. Similarly, the second block 44b is proximate to and
substantially parallel with the surface of the workpiece that is to
be machined so as to form the second longeron landing 30b.
Similarly, the third block 44c is proximate to and substantially
parallel with the surface of the workpiece that is to be machined
so as to form the third longeron landing 30c.
The positions of the blocks 44a-c in the second digital model may
be determined using the positions of the longeron landings 30a-c in
the first digital model.
In some embodiments, a coordinate measuring machine (CMM) is used
to inspect the locator pins 42 and/or the blocks 44a-c. The frame
machining fixture 40 may be further processed, i.e. adjusted, to
ensure that the frame machining fixture 40 is as specified by the
second digital model, for example, the locator pins 42 and/or the
blocks 44a-c may be further machined dependent upon the CMM
measurements. This processes of measuring and adjusting the
machining fixture may be performed iteratively.
At step s14, a coordinate measuring machine (CMM) measures the
relative locations of the fixture attachment features 32 of the
workpiece produced at step s8.
At step s16, using the CMM measurements of the fixture attachment
features 32 on the workpiece, a computer determines a datum,
hereinafter referred to as the "frame datum". The frame datum is a
reference system, with respect to the attachment features, from
which measurements may be made. The frame datum may be computed
using any appropriate software package, for example, the Valisys
(Trademark) software package.
At step s18, the CMM measures the surface of the workpiece with
respect to the frame datum. Thus, the locations of points on the
surface of the workpiece with respect to the fixture attachment
features 32 are determined.
At step s20, the workpiece is fixedly secured to the frame
machining fixture 40 by placing the workpiece onto the upper
surface of the base portion 41 such that each locator pin 42 is
coupled to (i.e. positioned through) a respective fixture
attachment feature 32. The locator pins 42 may be threaded and the
workpiece may be secured to the threaded locator pins 42 by
screwing nuts onto the threaded pins.
FIG. 6 is a schematic illustration (not to scale) showing a
top-down view of the workpiece 50 coupled to the frame machining
fixture 40.
The three portions of the workpiece 50 that are to be machined so
as to produce the longeron landings 30a-c are hereinafter referred
to as the "excess portions" and are indicated in FIG. 6 by hashed
regions and the reference numerals 52a-c. As shown in FIG. 6, the
blocks 44a-c provide surfaces that are proximate to and
substantially parallel with the surfaces of the workpiece 50 that
are to be machined to form the longeron landings 30a-c.
At step s22, while the workpiece 50 is attached to the frame
machining fixture 40, the 5-axis CNC milling machine machines the
workpiece so as to remove the excess portions 52a-c, thereby
forming the longeron landings 30a-c and producing the first
frame.
In this embodiment, the first excess portion 52a of the workpiece
50 is removed/machined so as to form the first longeron landing
30a. Also, the second excess portion 52b of the workpiece 50 is
removed/machined so as to form the second longeron landing 30b.
Also, the third excess portion 52c of the workpiece 50 is
removed/machined so as to form the third longeron landing 30c.
In this embodiment, the removal of the first excess portion 52a is
performed as follows.
Firstly, the 5-axis CNC milling machine probes the surface of the
first block 44a, for example, by moving so as to contact with the
surface of the first block 44a that is parallel with the surface of
the workpiece 50 to be machined. In this way, the CNC milling
machine determines the location of its cutting tool in space with
respect to the frame datum.
In this embodiment, the positional relationship between the blocks
44a-c and the locator pins 42 is known from the second digital
model. Also, when the workpiece 50 is coupled to the frame
machining fixture 40, the locator pins 42 are substantially
collocated with the fixture attachment features 32 of the workpiece
50. Thus, the positions of the blocks 40a-c with respect to the
frame datum are known. Thus, when CNC machine probes (i.e. contacts
with) the first block 44a, the position of the cutting tool with
respect to the frame datum is known/determined with relatively high
accuracy.
Secondly, using the known position of the cutting tool, the
measurements of the surface of the workpiece taken at step s18, and
the first digital model (which specifies the shape of the first
longeron landing 30a), the CNC machine machines away the first
excess portion 52a of the workpiece 50 so as to form the first
longeron landing 30a. In this embodiment, this machining is
performed by moving the cutting tool with respect to the frame
datum such that the first longeron landing 30a is formed with a
high degree of accuracy relative to the frame datum, i.e. the
fixture attachment features 32. Preferably, the cutting tool is
moved from the surface of the first block 44a that is parallel with
the surface of the workpiece 50 to be machined, in only a single
direction, i.e. along only a single axis. This limited movement of
the cutting tool from the block advantageously tends to reduce
errors.
The removal of the second and third excess portions 52b, 52c to
form the second and third longeron landings 30b, 30c respectively
is performed using an analogous method to that described above for
the forming of the first longeron landing 30a. Thus, in this
embodiment, the longeron landings 30a-c are formed with high
accuracy with respect to the frame datum (i.e. the fixture
attachment features 32).
Thus, a process of producing the first frame 8 is provided.
In some embodiments, measurements of the positions of the blocks
44a-c relative to the locator pins 42 may be used to determine the
positions of the blocks 44a-c in the frame datum.
In some embodiments, measurements of the surface of the frame
machining fixture 40 (e.g. taken using a CMM) are used to create
the "frame datum". For example, the frame datum may be created
using measurements of the locator pins 42 on the frame machining
fixture 40.
An embodiment of a process of producing the airframe 6 described in
more detail above with reference to FIG. 2 will now be
described.
FIG. 7 is a process flow chart showing certain steps of an
embodiment of a process of producing the airframe 6.
At step s32, an assembly jig is produced. A process of producing
the jig is described in more detail later below with reference to
FIG. 12.
FIG. 8 is a schematic illustration (not to scale) showing a
perspective view of an embodiment of the jig 60 produced at step
s32.
In this embodiment, the jig 60 comprises a steel jig frame 62
comprising a plurality of steel beams that are attached together
(e.g. by welding) to form a rectangular parallelepiped.
The jig 60 further comprises a steel reference frame 64 attached
(e.g. by welding) to one end of the jig frame 62. In this
embodiment, the reference frame 64 is, in effect, a copy of the
fore fuselage frame to which, during assembly of the aircraft 2,
the aft fuselage 4 is to be attached. In other words, the reference
frame 64 is substantially the same as the frame of the fore
fuselage 5 to which the second free ends 14b, 16b, 18b of the
longerons 14, 16, 18 are to be attached.
The jig 60 further comprises four sets of pickup devices,
hereinafter referred to as "jig pickups". Preferably, the jig
pickups are of universal construction. In this embodiment, each jig
pickup comprises a mounting element for mounting the device on the
jig frame 62, a receiving element for carrying an airframe
component, and a plurality of elongate members having predetermined
lengths connected together by means of clamping elements so as to
allow six degrees of freedom of movement of the receiving element
around three orthogonal axes. Examples of appropriate jig pickups
include, but are not limited to, those described in EP1230124 and
EP1600379, each of which is incorporated in its entirety herein by
reference. The pick-up devices may be formed from aluminium.
Each of the first set of jig pickups is indicated in FIG. 8 by the
reference numeral 66. Each of the second set of jig pickups is
indicated in FIG. 8 by the reference numeral 68. Each of the third
set of jig pickups is indicated in FIG. 8 by the reference numeral
70. Each of the fourth set of jig pickups is indicated in FIG. 8 by
the reference numeral 72.
As described in more detail later below with reference to FIG. 12,
the first jig pickups 66 are configured to securely hold the first
frame 8 in a predetermined position relative to the reference frame
64.
In this embodiment, each of the first jig pickups 66 is attached to
the jig frame 62, e.g. by bolts or welding. Attachment using bolts
advantageously tends to permit adjustment of the first jig pickups
66 so that their positions on the jig frame 62 are in accordance
with a digital model that specifies those positions, and also
allows for the removal of the first jig pickups 66 from the jig
frame 62. Each of the first jig pickups 66 comprises an elongate
arm to which is attached a receiving element 74, hereinafter
referred to as a "first receiving element". Each of the first
receiving elements 74 is configured to couple to a respective
fixture attachment feature 32 of the first frame 8.
For ease of illustration, only two first jig pickups 66 are shown
in FIG. 8. However, in reality, the number of first jig pickups 66
is such that the number of first receiving elements 74 is equal to
the number of fixture attachment features 32 of the first frame
8.
As described in more detail later below with reference to FIG. 12,
the second jig pickups 68 are configured to securely hold the
second frame 10 in a predetermined position relative to the
reference frame 64.
In this embodiment, each of the second jig pickups 68 is attached
to the jig frame 62, e.g. by bolts or welding. Each of the second
jig pickups 68 comprises an elongate arm to which is attached a
receiving element 76, hereinafter referred to as a "second
receiving element". Each of the second receiving elements 76 is
configured to couple to a respective attachment feature of the
second frame 10.
For ease of illustration, only two second jig pickups 68 are shown
in FIG. 8. However, in reality, the number of second jig pickups 68
is such that the number of second receiving elements 76 is equal to
the number of attachment features of the second frame 10.
As described in more detail later below with reference to FIG. 12,
the third jig pickups 70 are configured to securely hold the third
frame 12 in a predetermined position relative to the reference
frame 64.
In this embodiment, each of the third jig pickups 70 is attached to
the jig frame 62, e.g. by bolts or welding. Each of the third jig
pickups 70 comprises an elongate arm to which is attached a
receiving element 78, hereinafter referred to as a "third receiving
element". Each of the third receiving elements 78 is configured to
couple to a respective attachment feature of the third frame
12.
For ease of illustration, only two third jig pickups 70 are shown
in FIG. 8. However, in reality, the number of third jig pickups 70
is such that the number of third receiving elements 78 is equal to
the number of attachment features of the third frame 12.
As described in more detail later below with reference to FIG. 12,
the fourth jig pickups 72 are configured to securely hold the
second ends of the beams 20, 22 in a predetermined position
relative to the reference frame 64.
In this embodiment, each of the fourth jig pickups 72 is attached
to the jig frame 62, e.g. by bolts or welding. Each of the fourth
jig pickups 72 comprises an elongate arm to which is attached a
receiving element 80, hereinafter referred to as a "fourth
receiving element". Each of the fourth receiving elements 80 is
configured to couple to a respective attachment feature of a beam
20, 22.
For ease of illustration, only two fourth jig pickups 72 are shown
in FIG. 8. However, in reality, the number of fourth jig pickups 72
is such that the number of fourth receiving elements 80 is equal to
the number of attachment features of the beams 20, 22.
At step s34, each of the frames 8, 10, 12 are produced as described
in more detail earlier above with reference to FIG. 4.
At step s36, the frames 8, 10, 12 are attached to the jig 60.
In particular, in this embodiment the first frame 8 is attached to
the first jig pickups 66 such that each of the first receiving
elements 74 is coupled to a respective fixture attachment feature
32 of the first frame 8. Thus, the first frame 8 is fixedly
attached to the jig 60 at a predetermined position relative to the
reference frame 64. In this embodiment, as described in more detail
later below with reference to FIG. 12, the position on the jig 60
of the first frame 8 with respect to the reference frame 64 is the
same as the desired position on the assembled aircraft 2 of the
first frame 8 with respect to the fore fuselage frame.
Also, in this embodiment the second frame 10 is attached to the
second jig pickups 68 such that each of the second receiving
elements 76 is coupled to a respective attachment feature of the
second frame 10. Thus, the second frame 10 is fixedly attached to
the jig 60 at a predetermined position relative to the reference
frame 64. In this embodiment, as described in more detail later
below with reference to FIG. 12, the position on the jig 60 of the
second frame 10 with respect to the reference frame 64 is the same
as the desired position on the assembled aircraft 2 of the second
frame 10 with respect to the fore fuselage frame.
Also, in this embodiment the third frame 12 is attached to the
third jig pickups 70 such that each of the third receiving elements
78 is coupled to a respective attachment feature of the third frame
12. Thus, the third frame 12 is fixedly attached to the jig 60 at a
predetermined position relative to the reference frame 64. In this
embodiment, as described in more detail later below with reference
to FIG. 12, the position on the jig 60 of the third frame 12 with
respect to the reference frame 64 is the same as the desired
position on the assembled aircraft 2 of the third frame 12 with
respect to the fore fuselage frame.
At step s38, the beam 20 is attached to the jig 60 and the first
frame 8.
In this embodiment, the beam 20 comprises one or more attachment
features, i.e. through holes, proximate to its second end. In this
embodiment, the beam 20 is attached to the fourth jig pickups 72
such that each of the fourth receiving elements 80 is coupled to a
respective attachment feature of the beam 20. Also, the first end
of the beam 20 is attached, e.g. by bolts, to the first frame 8.
Thus, the beam 20 is fixedly attached to the jig 60 and the first
frame 8. In this embodiment, the beam 20 is attached to the jig 60
such that the second end of the beam 20 is at a predetermined
position relative to the reference frame 64. In this embodiment, as
described in more detail later below with reference to FIG. 12, the
position on the jig 60 of the second end of the beam 20 with
respect to the reference frame 64 is the same as the desired
position on the assembled aircraft 2 of the second end of the beam
20 with respect to the fore fuselage frame.
At step s40, the keels are attached between adjacent frames 8, 10,
12 e.g. by bolting. In this embodiment, the keels not directly
attached to the jig 60 e.g. by pickups, and instead are attached to
the frames 8, 10, 12 only.
At step s42, the longerons 14, 16, 18 are attached to the jig 60
and the first frame 8.
In particular, in this embodiment, the first longeron 14 is
attached to the first longeron landing 30a of the first frame 8, a
first longeron landing of the second frame 10, and a first longeron
landing of the third frame 12. Also, the second free end 14b of the
first longeron 14 may be attached to a feature of the reference
frame 64 that corresponds to a feature of the fore fuselage frame
to which, during assembly of the aircraft 2, the second free end
14b of the first longeron 14 is to be attached. In some
embodiments, the first free end 14a of the first longeron 14 may be
attached to the first frame 8 and/or the jig 60 e.g. to a jig
pickup.
Also, in this embodiment, the second longeron 16 is attached to the
second longeron landing 30b of the first frame 8, a second longeron
landing of the second frame 10, and a second longeron landing of
the third frame 12. Also, the second free end 16b of the second
longeron 16 may be attached to a feature of the reference frame 64
that corresponds to a feature of the fore fuselage frame to which,
during assembly of the aircraft 2, the second free end 16b of the
second longeron 16 is to be attached. In some embodiments, the
first free end 16a of the second longeron 16 may be attached to the
first frame 8 and/or the jig 60 e.g. to a jig pickup.
Also, in this embodiment, the third longeron 18 is attached to the
third longeron landing 30c of the first frame 8, a third longeron
landing of the second frame 10, and a third longeron landing of the
third frame 12. Also, the second free end 18b of the third longeron
18 may be attached to a feature of the reference frame 64 that
corresponds to a feature of the fore fuselage frame to which,
during assembly of the aircraft 2, the second free end 18b of the
third longeron 18 is to be attached. In some embodiments, the first
free end 18a of the third longeron 18 may be attached to the first
frame 8 and/or the jig 60 e.g. to a jig pickup.
As the longeron landings of the frames 8, 10, 12 have been machined
with high accuracy with respect to the fixture attachment features
32 of the frames 8, 10, 12 (i.e. to the frame datums), and the
frames 8, 10, 12 have been located on jig 60 at predetermined
positions with respect to the reference frame 64 using the fixture
attachment features 32 of the frames 8, 10, 12, when the longerons
14, 16, 18 are attached to the longeron landings, the longerons 14,
16, 18 tend to be accurately located at predetermined positions
with respect to the reference frame 64. In this embodiment, the
positions on the jig 60 of the longerons 14, 16, 18 with respect to
the reference frame 64 is the same as the desired position on the
assembled aircraft 2 of the third frame 12 with respect to the fore
fuselage frame.
A step s44, sacrificial plies or layers of material, which are
collectively referred to hereinafter as "packer material" are
applied, e.g. using an adhesive, to the surfaces of the airframe
components (i.e. the surfaces of the frames 8, 10, 12, the
longerons 14, 16, 18, and the beam 20) to which the aircraft skin
is to be attached.
In this embodiment, the packer material is applied to the airframe
components after the airframe 6 has been assembled in the jig 60.
However, in other embodiments, the packer material is applied to
the airframe components prior to the airframe 6 being assembled in
the jig 60.
Steps s46 to s50 of the process of FIG. 7 will be described in more
detail later below after a description of the packer material and
its application to the airframe components.
FIG. 9 is a schematic illustration showing packer material 90
applied to a surface of the first frame 8 and the first longeron
14.
The desired IML for the airframe 6 is shown in FIG. 9 as a dotted
line and is indicated by the reference numeral 92. The IML 92 may
be specified in the digital model of the airframe 6 or aft fuselage
4.
In this embodiment, the packer material 90 is made of a composite
material such as a fibre-reinforced polymer, i.e. a polymer matrix
reinforced with fibres (e.g. carbon or glass fibres). The packer
material 90 is a different material to that/those from which the
airframe components are made
In this embodiment, the packer material 90 is of sufficient
thickness to provide that desired IML 92 is at or beneath the outer
surface of the packer material 90. The thickness for the packer
material may be determined by performing a tolerance analysis using
a detail stage inspection of the components and determined assembly
tolerances. In some embodiments, the thickness of the packer
material is 1.75 mm to 2.29 mm, e.g. 2.03 mm.
In some embodiments, packer material 90 is not added to some or all
of the surfaces of the airframe components. For example, in some
embodiments, if the outer surface of an airframe component is
located at the desired IML 92, packer material 90 is not added to
that surface.
The application of the packer material 90 to the components of the
airframe 6 may be performed in any appropriate way. In some
embodiments, the packer material 90 comprises flat sheets which are
pressed against and attached to the components of the airframe 6.
Alternatively, the packer material 90 may be shaped to fit against,
i.e. be complementary to, the components of the airframe 6. For
example, the packer material 90 may be moulded into an appropriate
shape by applying the packer material 90 to a mould tool and curing
the packer material 90 in an autoclave.
FIG. 10 is a schematic illustration showing an example way in which
the packer material 90 may be applied to an outer surface of the
first frame 8.
In this embodiment, an adhesive 94 is used to adhere the packer
material 90 to the first frame 8. An over press tool 96 is used to
hold the packer material 90 in place while the adhesive 94 cures or
solidifies.
In this embodiment, the over press tool 96 comprises a rigid body
portion 98 (also referred to as a "strong back") and a deformable
portion 100. The body portion 98 is substantially non deformable.
The body portion 98 comprises a plurality of clamp receiving
elements 102 for receiving respective clamp devices 104 such as
G-clamps.
In use, the over press tool 96 is positioned onto a portion of the
airframe 6 such that packer material 90 is between the over press
tool 96 and the first frame 8, and such that the deformable portion
100 of the over press tool 96 is in contact with the packer
material 90. The over press tool 96 is then attached to and pressed
against the packer material 90 and first frame 8 using a plurality
of clamp devices 104 which engage with the clamp receiving elements
102 of the body portion 98 and the first frame 8. The over press
tool 96 remains in place until the adhesive 94 has cured and the
packer material 90 is securely attached to the first frame 8, at
which point the clamp devices 104 and the over press tool 96 are
removed.
In this embodiment, the over press tool 96 is shaped to be
complementary to a part of the first frame to which the packer
material is to be applied. The first digital model (i.e. the
digital model of the first frame 8) may be used to specify a shape
for the over press tool 96 and/or specify a digital model for
producing the over press tool 96. The body portion 98 may then be
produced using an appropriate process, such as an Additive Layer
Manufacturing (ALM) process, from any appropriate material, such as
plastic.
The deformable portion 100 advantageously tends to provide that the
force exerted by the over press tool 96 onto the packer material 90
is substantially evenly distributed. Furthermore, the deformable
portion 100 tends to facilitate the use of the over press tool 96
in cases where there are assembly positioning errors etc.
In this example, the over press tool 96 is held against the packer
material 90 and first frame 8 using a plurality of clamp devices
104. However, in other examples, the over press tool 96 may be held
against the packer material 90 and an airframe component in a
different way.
FIG. 11 is a schematic illustration showing a further example way
in which the packer material 90 may be applied to an outer surface
of the first frame 8.
In this embodiment, the over press tool 96 further comprises a
rigid arm 106 connecting the body portion 98 to an actuation device
108. The actuation device 108 may, for example be a pneumatic or
hydraulic actuation device 108 configured to actuate the over press
tool 96. The over press tool 96 further comprises a vacuum line 110
connecting the surface of the deformable portion 100 to a vacuum
pump 112.
In operation, the first frame 8 is securely held by a support
structure 114 (e.g. the jig 60). The packer material 90 is held
onto the deformable portion 100 of the over press tool 96 by
establishing a vacuum in the vacuum line 110. The over press tool
96 is then actuated by the actuation device 108 in such a way that
the packer material 90 coupled to the over press tool 96 is brought
into contact with the first frame 8 (i.e. the over press tool 96 is
moved in the direction of the arrows in FIG. 11) and firmly pressed
against the first frame 8 until the adhesive 94 cures. The vacuum
holding the packer material 90 to the over press tool 96 may then
be released and the over press tool 96 may be moved away from the
first frame 8 leaving the packer material 90 adhered thereto.
Having the packer material 90 be retained against the over press
tool 96 and subsequently bringing the packer material 90 coupled to
the over press tool 96 into contact with the first frame 8 (as
opposed to applying the packer material 90 to the first frame and
subsequently bringing the over press tool into contact with the
packer material 90 on the first frame 8) advantageously tends to
reduce unwanted movement of the packer material 90 with respect to
the first frame 8. For example, a likelihood of the packer material
90 that is applied to the first frame 8 moving with respect to the
first frame 8 when the over press tool 96 is brought into contact
with the packer material 90 on the first frame 8 tends to be
reduced or eliminated. Thus, accuracy with which packer material 90
is applied to an object tends to be increased.
Furthermore, having the packer material 90 be retained against the
over press tool 96 and subsequently bringing the packer material 90
coupled to the over press tool 96 into contact with the first frame
8 tends to reduce the likelihood of the packer material 90 adhering
to the first frame 8 before a pressing force is applied. This tends
to improve adherence of the packer material to the object.
Returning now to the process of FIG. 7, at step s46, optionally, a
laser tracker or CMM is used to measure the outer surface of the
packer material 90 that has been applied to the components of the
airframe 6. In this embodiment, the outer surface of the packer
material 90 is measured with respect to a so-called "jig datum"
which will be described in more detail later below with reference
to FIG. 12. In some embodiments, this step may be omitted or may be
performed at a later stage.
At step s48, a CNC cutting device is used to machine the packer
material 90 such that the outer surface of the packer material 90
is located at the IML 92 specified in the digital model of the
airframe 6 or aft fuselage 4 with respect to the fore reference
frame 64. Optionally, this may be performed using the laser tracker
measurements taken at step s46. In this embodiment, the CNC cutting
device is controlled with respect to the "jig datum" *which is
described in more detail later below.
Thus, the packer material 90 is machined to allow for variations in
component thicknesses and substructure assembly positioning errors.
This tends to provide that, when the aircraft skin is attached to
the airframe 6, the OML of the aft fuselage 4 is within the
pre-specified tolerance with respect to the fore reference frame 4
(i.e. fore fuselage in the assembled aircraft 2). Furthermore, the
machined packer material 90 provides a consistent landing surface
to which the aircraft skin may be fixed. The landing surface
provided by the machined packer material 90 is accurately
positioned with respect to the jig datum.
Use of the sacrificial packer material 90 advantageously tends to
reduce or eliminate a need to machine the surfaces of the airframe
components (i.e. the surfaces of the frames 8, 10, 12, the
longerons 14, 16, 18, and the beam 20) to which the aircraft skin
is to be attached. Thus, a need for performing post-machining
analysis/testing of the airframe components may be avoided or
reduced.
Use of the packer material 90 advantageously tends to reduce or
eliminate a need for shims to be applied to fill gaps between the
airframe 6 and the external aircraft skin when the aircraft skin is
attached to the airframe 6.
Steps s46 and s48 may be performed iteratively.
Thus, the airframe 6 is assembled using the jig 60.
At step s50, the assembled airframe 6 may be removed from the jig
60.
Thus, an embodiment of a process of producing the airframe 6 is
provided.
Returning now to the process of producing the jig 60 performed at
step s32, FIG. 12 is a process flow chart showing certain steps of
an embodiment of a process of producing the jig 60.
At step s50, a plurality of steel beams are attached together, e.g.
by welding, to form a rectangular parallelepiped, thereby producing
the jig frame 62. An example jig frame and method of construction
thereof includes, but is not limited to, those described in
EP1230124 and EP1600379, each of which is incorporated in its
entirety herein by reference. The pick-up devices may be formed
from aluminium.
At step s52, the reference frame 64 is attached, e.g. by welding,
to one end of the jig frame 62. In this embodiment, the reference
frame 64 is a substantially exact replica of at least part of the
fore fuselage frame to which the airframe 6 of the aft fuselage 4
is to be attached.
At step s54, a CMM measures a surface of the reference frame 64 on
the jig 60. In particular, in this embodiment, the CMM measures
features of the reference frame 64 that correspond to those
features of the fore fuselage frame to which the airframe 6 is to
be attached.
At step s56, using the CMM measurements of the reference frame 64,
a computer determines a datum, herein referred to as the "jig
datum". The jig datum is a reference system, with respect to the
reference frame 64, from which measurements may be made. The jig
datum may be computed using any appropriate software package.
At step s58, a human designer generates or creates a further
digital model, hereinafter referred to as the "third digital
model". The third digital model is of the airframe and the fore
fuselage frame. The third digital model specifies the positional
relationships between the components of the airframe 6 and the fore
fuselage frame, when the airframe 6 is attached to the fore
fuselage frame.
The third digital model may be created using a computer and an
appropriate software package, for example, the Catia (Trademark) V4
software package.
At step s60, using the third digital model, the human designer or a
computer determines positions on the jig frame 60 for each of the
jig pickups 66, 68, 70, 72.
In this embodiment, the determined locations on the jig 60 of the
first jig pickups 66 are such that, were the first frame 8 to be
held by the first jig pickups 66, the position of the first frame 8
relative to the reference frame 64 would be substantially the same
as a desired position for the first frame 8 relative to the fore
fuselage frame onboard the assembled aircraft 2.
Similarly, the determined locations on the jig 60 of the second jig
pickups 68 are such that, were the second frame 10 to be held by
the second jig pickups 68, the position of the second frame 10
relative to the reference frame 64 would be substantially the same
as a desired position for the second frame 10 relative to the fore
fuselage frame onboard the assembled aircraft 2.
Similarly, the determined locations on the jig 60 of the third jig
pickups 70 are such that, were the third frame 12 to be held by the
third jig pickups 70, the position of the third frame 12 relative
to the reference frame 64 would be substantially the same as a
desired position for the third frame 12 relative to the fore
fuselage frame onboard the assembled aircraft 2.
Similarly, the determined locations on the jig 60 of the fourth jig
pickups 72 are such that, were the second ends of the beams 20, 22
held by the fourth jig pickups 72, the positions of the second ends
of the beams 20, 22 relative to the reference frame 64 would be
substantially the same as a desired position for the second ends of
the beams 20, 22 relative to the fore fuselage frame onboard the
assembled aircraft 2.
At step s62, each of the jig pickups 66-72 are attached to the jig
frame 62, e.g. by bolts or by welding, in the position determined
at step s60 for that jig pickup.
Steps s64 and s66 are optional steps for verifying and, if
necessary, adjusting the position and/or orientation of the jig
pickups on the jig 60. In some embodiments, these steps are omitted
or a different verification and/or different adjustment process is
performed. Steps s64 and s66 may be performed iteratively.
At step s64, a laser tracker measures the position of each of the
jig receiving elements 74-80 with respect to the jig datum, i.e.
with respect to the fore reference frame 64.
At step s66, using the laser tracker measurements, the positions of
the jig receiving elements 74-80 with respect to the jig datum may
be modified to ensure that each of the jig receiving elements 74-80
has the position determined at step s60 for that jig receiving
element 74-80. In other words, the positions of the jig receiving
elements 74-80 may be modified to ensure that, when the frames 8,
10, 12 are held by the jig receiving elements 74-80, the positions
of the frames 8, 10, 12 relative to the reference frame 64 are
substantially the same as a desired position for the frames 8, 10,
12 relative to the fore fuselage frame onboard the assembled
aircraft 2.
Modifying a position of a jig receiving element 74-80 may be
performed by, for example, introducing a shim between a jig pickup
and the jig frame 62, or by machining part a jig pickup and/or the
jig frame 62.
In some embodiments, the positions of one or more of the jig
pickups 66, 68, 70, 72 measured by the laser tracker may be used to
update or recalculate the jig datum. For example, in some
embodiments, a new jig datum is calculated using measured positions
of the reference frame and one or more of the jig receiving
elements 74-80. This new jig datum is a reference system, with
respect to the reference frame 64 and one or more of the jig
receiving elements 74-80, from which measurements may be made.
Thus, an embodiment of a process of producing the jig 60 is
provided.
An advantage provided by the above described methods and apparatus
is that the airframe advantageously is produced within very tight
tolerance bounds that tend not to be possible using conventional
production techniques. The airframe is produced with high accuracy
relative to the reference frame which is representative of a
forebody frame to which the airframe is to be attached. In
particular, the airframe is produced such that the IML is within
very with tight tolerances with respect to the reference frame.
Thus, the assembly of the aircraft, and in particular the attaching
together of the aft fuselage and the fore fuselage, tends to be
facilitated.
Advantageously, the blocks of the frame machining fixture are
precision ground with respect to the locator pins of the frame
machining fixture (i.e. the frame datum). During production of the
frame, each block is used as a "zero point" from which a cutting
tool is moved to machine a respective frame longeron landing close
to that block. The proximity of the block to the associated
longeron landing advantageously tends means that, in order to form
a longeron landing, the cutting tool does not have to be moved
large distances from a "zero point". Thus, errors tends to be
reduced and the accuracy (with respect to the frame datum) with
which the longeron landings are formed tends to be increased.
Advantageously, the above described jig tends to use fewer pickups
for holding the airframe components compared to conventional
assembly jigs. Thus, the weight and cost of the jig tends to be
reduced compared to conventional assembly jigs. Furthermore, as
airframe components are held by fewer pickups, damage/stresses
resulting from a component being held by pickups tends to be
reduced.
Advantageously, the longeron landings of the frames are machined
with high accuracy with respect to a local frame datum that is
defined by frame features that are used to locate that frame in the
assembly jig. Thus, because the jig pickups that couple to the
frame attachment features are accurately located on the jig in a
desired position with respect to the reference frame, when the
frames are attached to the jig, the longeron landings are
accurately located on the jig in a desired position with respect to
the reference frame. Thus, when the longerons are attached to the
longeron landings of the frames, the longerons tend to be are
accurately located on the jig in a desired position with respect to
the reference frame. Accordingly, gaps or spaces between longerons
and frames advantageously tend to be minimised. The use shims to
fill such gaps or spaces tends to be reduced or eliminated.
The above described methods and apparatus tends to provide that the
frames of the airframe may be produced independently from one
another. In other words, there tends to be no requirement to
machine or process the frames as a set. This independent production
of the frames tends to reduce production time of the airframe
compared to conventional processes.
A further advantage provided by the above described methods and
apparatus is that non-destructive testing and other processes may
be performed on individual airframe components separately. This
tends to be difficult if, in contrast to the above described
method, multiple airframe components are machined as a set in an
assembly jig.
Apparatus, including the any of the abovementioned computers or
processes for performing any of the above described data processing
method steps may be provided by configuring or adapting any
suitable apparatus, for example one or more computers or other
processing apparatus or processors, and/or providing additional
modules. The apparatus may comprise a computer, a network of
computers, or one or more processors, for implementing instructions
and using data, including instructions and data in the form of a
computer program or plurality of computer programs stored in or on
a machine readable storage medium such as computer memory, a
computer disk, ROM, PROM etc., or any combination of these or other
storage media.
It should be noted that certain of the process steps depicted in
the flowcharts of FIGS. 4, 7, and 9 and described above may be
omitted or such process steps may be performed in differing order
to that presented above and shown in FIGS. 4, 7, and 9.
Furthermore, although all the process steps have, for convenience
and ease of understanding, been depicted as discrete
temporally-sequential steps, nevertheless some of the process steps
may in fact be performed simultaneously or at least overlapping to
some extent temporally.
In the above embodiments, an airframe of an aircraft aft fuselage
is produced. However, in other embodiments, a different type of
structure is produced, for example a structure that, in use, is to
be attached to a different structure may be produced. For example,
an airframe of a different part of the aircraft, e.g. the fore
fuselage, may be produced. In such embodiments, the jig may
comprise a different type of reference frame representing a
different type of entity to which the structure being assembled is
to be attached.
In the above embodiments, the aircraft comprises three frames,
three longerons, two beams, and a plurality of keels. However, in
other embodiments, the airframe comprises a different number of
frames, longerons, beams, and/or keels. In some embodiments, one or
more of the listed types of airframe components may be omitted. In
some embodiments, the airframe comprises a different type of
airframe component instead of or in addition to those listed
above.
In the above embodiments, a frame comprises four attachment
features which are used to determine the frame datum. The frame
attachment features are holes through the structure of the frame.
Also, the jig comprises jig pickups configured to attach to the
frame attachment features. Also, the frame machining fixture
comprises locator pins configured to couple to the frame attachment
features. However, in other embodiments, one or more of the frames
or other airframe components comprises a different number of
attachment features. In some embodiments, one or more of the
attachment features may be a different type of attachment feature
other than a through hole. Also, the jig may comprise a different
type of pickup that is configured to attach to the different type
of attachment feature. For example, in some embodiments, an
attachment feature may be a block-like structure and a jig pickup
may comprise a clamp for clamping to the block-like structure.
Also, the frame machining fixture may comprise a different type of
device that is configured to attach to the different type of
attachment feature.
In the above embodiments, longeron landings are machined with
respect to a local frame datum. However, in other embodiments one
or more different types of frame features are formed with respect
to the frame datum instead of or in addition to one or more of the
longeron landings.
In the above embodiments, the airframe components are made of
aluminium. However, in other embodiments, one or more of the
airframe components is made of a different type of material.
In the above embodiments, the jig frame is a steel beam frame in
the shape of a rectangular parallelepiped. However, in other
embodiments, the jig frame is made of a different material and/or
is a different shape.
In the above embodiments, the frame machining fixture comprises
three blocks which are used as reference points or surfaces from
which a CNC cutting tool is moved. The blocks are located on an
upper surface of the frame machining fixture. In other embodiments,
the frame machining fixture comprises a different number of blocks
or other devices that provide the above described functionality. In
some embodiments, one or more of the blocks is located on a
different part of the frame machining fixture, e.g. on a side of
the base portion.
* * * * *